V0.4.0

更新记录：

1. 🎉 终于支持设置字体和字号啦🙊🙊🙊🙊
2. 🍭 优化黑暗模式的展示，比之前更黑一些了
3. 🍭 代码支持pre标签、增加淡化背景、视觉展示优化
4. 🏂 支持复制的图片可以粘贴、默认宽度优化、编辑和预览切换优化
5. 🛠 修复预览模式下标题还可以编辑的问题

Update Notes：

1. 🎉 Support setting font and font size. 🙊🙊🙊🙊
2. 🍭 Optimize the presentation of dark mode,Darker than before.
3. 🍭 The code supports pre tags, adds fade background, and optimizes visual presentation.
4. 🏂 The copied pictures can be pasted, default width optimization, editing and preview switching optimization.
5. 🛠 Fix the problem that the title can be edited in preview mode.